1. Field of the Invention
The present invention relates to a centrifugal blower, and more particularly to a centrifugal blower for use in air conditioning units for motor vehicles.
2. Description of the Related Art
Heretofore, air conditioning units for motor vehicles have employed a centrifugal blower comprising a fan for introducing air from outside or inside of the motor vehicle, an electric motor for rotating the fan, and a casing housing the fan therein.
When the fan is rotated by the electric motor, air flows through a spiral air passage defined in the casing around the fan at a predetermined rate toward the passenger compartment of the motor vehicle. In order to increase the rate at which air flows toward the passenger compartment, the spiral air passage has its cross-sectional area progressively greater from an end thereof close to the electric motor where the spiral turn of the air passage begins toward another end thereof where the spiral turn of the air ends. Also, the casing has a slanted surface lying along an angle at which air is discharged from the centrifugal blower. The slanted surface includes a twisted surface whose angle with respect to a substantially horizontal plane is progressively greater from the electric motor toward the outlet of the centrifugal blower. For details, reference should be made to Japanese Laid-Open Patent Publication No. 9-158898, for example.
Recently, there has been a demand for a further increase in the rate of the air flow from the inlet toward outlet of the casing in the centrifugal blower. One solution is to increase the output power of the electric motor which rotates the fan to increase the rate of the air flow discharged by the fan out of the centrifugal blower. However, increasing the output power of the electric motor naturally tends to increase the size of the electric motor and hence the cost thereof, resulting in an increase in the overall size of the centrifugal blower.